1. Field of the Invention
The present invention relates to an apparatus for plasma-processing a target object in the semiconductor processing system by using a plasma and, more particularly, to an inductive coupling type dry etching apparatus whose processing chamber is divided into a plasma generating space and a processing space. Note that semiconductor processing means various types of processing operations performed to manufacture, on a target object, e.g., a semiconductor wafer or an LCD substrate, semiconductor devices and structures including wiring layers and electrodes to be connected to the semiconductor devices by forming semiconductor layers, insulating layers, conductive layers, and the like on the target object with predetermined patterns.
2. Discussion of the Background
As a plasma processing apparatus in the semiconductor processing system, one is known in which the interior of its airtight processing chamber is divided into a plasma generating space and a processing space by a grid electrode formed with a large number of through holes. An inductive coupling type dry etching apparatus is available as an example of such a plasma processing apparatus. This dry etching apparatus has an RF (radio-frequency) antenna opposing the plasma generating space through a dielectric wall. In the etching apparatus of this type, a process performed when etching an oxide film (SiO.sub.2 film) formed on the surface of a target object, i.e., a semiconductor wafer, is as follows.
First, the target object is placed on a lower electrode arranged in the processing space. Subsequently, the interior of the processing chamber is evacuated by an exhaust system connected to the processing space, thereby setting the entire portion of the interior of the processing chamber to a predetermined pressure-reduced atmosphere. While the interior of the processing chamber is continuously evacuated, a gas mixture of a process gas such as an inert gas, e.g., Ar, He, or Kr, and a reactive gas, e.g., CF.sub.4, C.sub.4 F.sub.8, or CHF.sub.3, is supplied from a process gas supply system to the plasma generating space.
In this state, a plasma generating RF power is applied to the RF antenna so that the process gas supplied to the plasma generating space is excited and dissociated, thereby generating a high-density plasma. Simultaneously, a bias RF power is applied to the lower electrode to guide, through the grid electrode, an etchant in the plasma, e.g., CFx radicals, onto the oxide film on the surface of the wafer arranged in the processing space. Only a desired etchant in the plasma is introduced into the processing space by the grid electrode arranged as described above between the plasma generating space and the processing space, thereby etching the wafer.
The etching apparatus described above can perform etching at a high etching rate because it can generate a high-density plasma. On the other hand, dissociation of the reactive gas, e.g., CF-based gas, progresses excessively to sometimes degrade the etching selectivity of the oxide film. This poses a problem particularly when forming a contact hole having a high aspect ratio in a thick oxide film.